Over-voltage protection for voltage regulator modules of a parallel power system

ABSTRACT

A protection circuit for a parallel power system having at least two parallel coupled voltage regulators is disclosed. The protection circuit includes at least two isolation control circuits, each control circuit being coupled to a respective voltage regulator. Each isolation control circuit includes a current sense circuit for sensing current polarity at an output of the respective voltage regulator, and a controller for automatically isolating the respective voltage regulator when an over-voltage condition exists at an output of the parallel power system and a positive current polarity is sensed at the output of the respective voltage regulator. The at least two isolation control circuits isolate only a voltage regulator having positive current outflow during the over-voltage condition. In one embodiment, each isolation control circuit further includes an over-voltage detection circuit for detecting when the over-voltage condition exists at the output of the parallel power system.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/199,644, filed Aug. 9, 2005, entitled “Over-VoltageProtection for Voltage Regulator Modules of a Parallel Power System”, byCovi et al., the entirety of which is hereby incorporated herein byreference.

TECHNICAL FIELD

This invention relates generally to parallel computer power supplysystems, and more particularly, to an over-voltage protection circuitand method for a parallel power supply system.

BACKGROUND OF THE INVENTION

Computer systems typically utilize parallel power supply systems. Aparallel power supply system generally comprises a plurality of powersources such as DC-DC converters or voltage regulators connected inparallel to provide current to a load comprising one or more processors,memory devices, disk drives, etc.

Existing parallel power supplies employing PWM topologies allow “burstmode” which terminates switching on a properly functioning regulatormacro in the presence of an over-voltage caused by a parallel regulatormacro. This lack of switching is detectable and allows logic gates todiscern which macro is the offending over-voltage producer (i.e., isactively switching), and correctly disable it. One example of such acircuit is described in U.S. Pat. No. 6,278,597 entitled “ConditionalOver-Voltage Protection for Redundant Phase-Shift Converters.”

Parallel voltage regulator modules (VRMs) are a new power systemtopology. Existing VRM parallel topologies do not protect well andtypically only terminate switching activity on a faulty phase. However,if the over-voltage condition is due to a shorted high-side switch in anon-insolated topology (as opposed to a control loop or referencefault), then simply terminating switching activity does not remove theover-voltage fault, which compromises the redundant purpose.

Certain existing VRM parallel topologies make use of the well-defined“Intel Load Line” that droops more than 5 percent of nominal voltage atfull load. By coordinating a sliding over-voltage threshold with loadcurrent, a VRM macro supporting load current would have a lower triggerthreshold for an over-voltage trip and therefore be the first VRM of theparallel group to trip. VRMs not providing load (properly functioning inthe presence of a over-voltage caused by a parallel macro) would have ahigher trigger threshold and thus protect properly. This solution lackstwo properties, however. First, light load conditions make theover-voltage thresholds identical for good and bad parallel VRMs, andsecondly, for load line droop of certain technology, which can be 10×less than that of Intel requirements, the over-voltage trigger thresholdis only fractions of a percent different between faulty VRMs andproperly functioning VRMs, even at substantial load conditions.

Accordingly, a parallel power supply protection circuit is needed whichcan accurately isolate a particular voltage regulator module that iscausing an over-voltage condition without causing a shut down of theentire parallel power system. The present invention meets this need.

SUMMARY OF THE INVENTION

The shortcomings of the prior art are overcome and additional advantagesare provided through a protection circuit for a parallel power systemhaving at least two parallel coupled voltage regulators. The protectioncircuit includes at least two isolation control circuits. Each isolationcontrol circuit is coupled to a respective voltage regulator of theparallel power system, and includes a current sense circuit and acontroller. The current sense circuit senses current polarity at anoutput of the respective voltage regulator, while the controllerautomatically isolates the respective voltage regulator when anover-voltage condition exists at an output of the parallel power systemand a positive current polarity is sensed at the output of therespective voltage regulator. The at least two isolation controlcircuits of the protection circuit function to isolate only a voltageregulator having positive current outflow during the over-voltagecondition.

In another aspect, a parallel power system is provided. This parallelpower system includes at least two voltage regulators coupled inparallel, and at least two isolation control circuits. Each isolationcontrol circuit is coupled to a respective voltage regulator of theparallel power system, and each circuit includes a current sense circuitand a controller. The current sense circuit senses current polarity atan output of the respective voltage regulator, while the controllerautomatically isolates the respective voltage regulator when anover-voltage condition exists at an output of the parallel power systemand a positive current polarity is sensed at the output of therespective voltage regulator. Together, the at least two isolationcontrol circuits of the protection circuit function to isolate only avoltage regulator having positive current outflow during theover-voltage condition.

In a further aspect, a method of protecting a parallel power supplyhaving at least two parallel coupled voltage regulators is provided. Themethod includes: providing a separate isolation control circuit for eachrespective voltage regulator of the at least two voltage regulators.Each isolation control circuit includes logic for: sensing currentpolarity at an output of the respective voltage regulator; andautomatically controlling isolation of the respective voltage regulatorwhen an over-voltage condition exists at an output of the parallel powersystem and a positive current polarity is sensed at the output of therespective voltage regulator, wherein only a voltage regulator havingpositive current outflow during the over-voltage condition is isolated.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts a typical parallel power supply configuration;

FIG. 2 is a simplified schematic diagram of a power supply systemcomprising a single multi-phase VRM and one embodiment of an isolationcontrol circuit, in accordance with an aspect of the present invention;

FIG. 3 is a simplified schematic diagram of one embodiment of a parallelpower supply system employing a plurality of multi-phase VRMs coupled inparallel, each with its own isolation control circuit, in accordancewith an aspect of the present invention;

FIG. 4 is a simplified schematic diagram of one embodiment of anisolation control circuit, shown coupled between an isolation fieldeffect transistor (FET) and an OR-ing FET connected at the input andoutput, respectively, of a voltage regulator module (not shown) of apower supply system such as depicted in FIGS. 2 & 3, in accordance withan aspect of the present invention; and

FIG. 5 is a flowchart of one embodiment of isolation control processingfor a voltage regulator module, in accordance with an aspect of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to an over-voltage protection circuit fora parallel power system. The following description is presented toenable one of ordinary skill in the art to make and use the inventionand is provided in the context of a patent application and itsrequirements. Various modifications to the preferred embodiment and thegeneric principles and features described herein will be readilyapparent to those skilled in the art. Thus, the present invention is notintended to be limited to the embodiment shown, but is to be accordedthe widest scope consistent with the principles and features describedherein.

The present invention is disclosed in the context of a preferredembodiment. The present invention provides for an over-voltageprotection circuit for a parallel power system. Through the use of acircuit or logic in accordance with the present invention, electronicdevices powered by the system are protected against being damaged as theresult of an over-voltage condition in one of the voltage regulatormodules. Moreover, the over-voltage protection circuit in accordancewith the present invention will not cause a shut down of the entiresystem should a voltage regulator experience an over-voltage condition.This results in a more stable and continuous operating environment.

More particularly, disclosed herein are techniques for detecting andisolating an over-voltage condition in any VRM topology, andparticularly, one that employs multiple parallel VRM macros. Forover-voltage protection in redundant, parallel VRM macros, a significantfeature is the ability to detect just the over-voltage offender and todisable just that VRM macro. The difficulty lies with all macrosreporting the same output voltage, how to determine which is theoffending macro. As disclosed herein, output current polarity isemployed to identify the offending macro. This is achieved by utilizingthe already existing OR-ing FET at the output of each VRM macro.Further, provision is made for isolating a faulty VRM macro in aredundant multi-phase VRM design that allows continued operation in theremaining VRM macros in the presence of a shorted FET, or other voltageregulation loop fault, creating an over-voltage from the faulty VRMmacro.

FIG. 1 depicts a typical parallel power supply configuration 100. Thisconfiguration 100 includes an input voltage 112, a fuse 114, a siliconcontrolled rectifier (SCR) 116, two parallel coupled VRMs 118, 120, athreshold voltage 122, a comparator 123, and a latch 124. A problemarises in this configuration when one of the VRMs in parallel initiatesan over-voltage (OV) condition. When one of the VRMs 118, 120 goes OV,it turns on the SCR 116 which can blow the fuse 114 and cause the entiresystem to shut down. The system also lacks the ability to detect whichVRM is creating the over-voltage condition. Further, noisy conditionsproduced by comparator 122 could cause the blowing of fuse 114. Oncethis happens, the VRMs will be without input power and the system willbe forced to shut down. For many applications, this is not a desirableoutcome.

Accordingly, there is a need in the art for a circuit which can isolatea particular voltage regulator that is in over-voltage condition, andshut only that over-voltage regulator down. Also, the circuit shouldaccomplish this without causing a shut down of the entire power system.

FIG. 2 is a depiction of a power system 200 that includes a multi-phasevoltage regulator module (VRM) 210 and a protection circuit inaccordance with an aspect of the present invention. The protectioncircuit combines an over-voltage detection circuit with a currentsensing circuit for sensing positive or negative current flow from theVRM module. A VRM with positive current outflow is identified as afaulty VRM during an over-voltage condition. The synchronous rectifierdesign of today's VRMs ensures that all other properly functioning VRMswill be sinking current, thus making detection of the one or more faultyVRMs absolutely conclusive, even in the presence of zero system loadcurrents. A further part of the implementation is a means to disconnectall power from the non-isolated VRM since a high-side switch short mustalso be protected from sustaining an output over-voltage.

In the embodiment of FIG. 2, the protection circuit comprises anover-voltage and current sense controller 260, which gates an isolationFET 230 at the input of multi-phase VRM 210, and which senses thepolarity across an OR-ing FET 240 located at the output of multi-phaseVRM 210. Operationally, an input bus 220, such as a 12-volt input bus,powers VRM 210, which although shown as a multi-phase VRM, couldalternatively comprise a single-phase VRM. In normal operation, powerfrom input bus 220 is applied across the input of VRM 210 sinceisolation FET 230 is gated ON. Output from VRM 210 is the desiredvoltage level, which can typically range from one volt to 12 volts,depending on the load 250 technology, which is shown in the drawing as asimple RC circuit. The OR-ing FET 240 at the output of VRM 210 isnormally gated ON and principally exists in the circuit to sense for anoutput short in the VRM. This FET 240 protects against an output shortto ground situation. In accordance with the present invention, however,FET 240 is also employed to facilitate sensing the direction of currentflow at the output of VRM 210. Controller 260 thus employs over-voltagedetection, by comparison of the load voltage with a reference value(Vref), as well as a current-sense polarity determination at the outputof VRM 210. Depending on the values of these determinations, thecontroller may gate isolation FET OFF in order to isolate a faulty VRM,as explained further below.

FIG. 3 depicts one example of a redundant, parallel power systememploying multiple multi-phase VRMs 210 connected in parallel to supplyan electronic load 250, such as a processor module. This parallel powersystem implementation employs, by way of example, the same isolationcircuitry embodiment as depicted in FIG. 2, with the over-voltage andcurrent sense controls 260 shown depicted within the VRMs 210 as oneexample only. These controls 260 could alternatively reside external tothe VRMs 210, such as shown in FIG. 2. In accordance with an aspect ofthe present invention, each VRM 210 has a detection and isolationcircuitry so that no single point of failure across the parallel powersystem exists.

FIG. 4 is a more detailed depiction of one hardware embodiment of theover-voltage and current sense controls 260 employed in FIGS. 2 & 3. Asshown, in this embodiment, over-voltage detection is performed by acomparator 400 which compares the output voltage of the power system,i.e., the voltage at the load, with a threshold or reference voltageVref. If the output voltage is greater than the reference voltage, thenan over-voltage condition is detected. In an alternate embodiment,over-voltage detection could be a centrally implemented function formultiple isolation control circuits, with an appropriate over-voltagecontrol signal being provided to each controller upon detection of theover-voltage condition, if such a single point of failure could betolerated.

A separate comparator 410 senses voltage polarity across the OR-ing FET240. If current flows out from the associated VRM (see FIGS. 2 & 3) thisoutflow is sensed by comparator 410 and an appropriate signal isprovided to a latching NAND circuit 420. If both the over-voltagecondition exists, and current flows out from the associated VRM, thenNAND circuit 420 gates OFF isolation FET 230. This functioning isdepicted in the flowchart of FIG. 5.

A single phase of a multi-phase VRM typically combines a PWM controller,a control FET, a synchronous FET, and an output inductor, as is known inthe art. Referring to the logic chart of FIG. 5, if one VRM control FETis shorted or maintained ON for a longer period than is required, thenan over-voltage may arise 500. The current polarity at the output ofeach VRM of a parallel power system is monitored to determine which VRMis sourcing current to the load 510. Further, each protection circuitdetermines that an over-voltage condition exists, indicating that anover-voltage fault is present 520. As a variation on this step, theover-voltage condition could be globally determined with a controlsignal being forwarded to each isolation circuit. A logical AND withineach protection circuit determines whether both conditions exist, and ifso, latches the associated isolation FET OFF at the input to therespective VRM 530.

To summarize, the protection scheme presented herein employs an outputOR-ing FET in a detection technique for determining whether or not theassociated VRM is supporting load current during an over-voltagecondition. Since all VRMs see the same output voltage, and all detectthe presence of an over-voltage condition when such a fault exists,determining whether or not the associated VRM is supporting load currentindicates which VRM is faulty. The output OR-ing FET is already anessential part of a redundant solution since it is necessary to preventa shorted low-side switch fault. The OR-ing FET drive is also designedfor fast switching, and forward versus reverse current flow detection tosupport its purpose of low-side switch fault isolation. (A positivecomparator 410 output represents current flowing out of the VRM.) Thus,current flow polarity sensing, when combined with over-voltage sensing,determines which is the faulty VRM to be isolated. A special VRMsynchronous rectifier property is used. Properly functioning VRMs in thepresence of an over-voltage will actually sink current. This makescurrent flow detection a very binary characteristic that is not relatedto system load current. Even at virtually zero system load, a faultyover-voltage producing VRM will be sourcing current into the properlyworking remaining VRMs that will be sinking current. The final part ofthe implementation is a means to disconnect all power from thenon-isolated VRM, since a high-side switch short must also be protectedfrom sustaining an output over-voltage.

Advantageously, through the use of a protection scheme in accordancewith the present invention, the load is protected against being damagedas a result of an over-voltage condition in one or more the voltageregulator modules. Moreover, over-voltage protection in accordance withthe present invention isolates the voltage regulator module that isexperiencing an over-voltage condition and shuts it down, withoutshutting down the entire system. This results in a more stable andcontinuous operating system.

As an enhancement, a micro-controller could be employed in place of thehardware controller embodiment of FIG. 4. In such a case, a currentlimiting electronic breaker could be used at the input to the associatedvoltage regulator.

Thus, the capabilities of one or more aspects of the present inventioncan be implemented in software, firmware, hardware or some combinationthereof.

One or more aspects of the present invention can be included in anarticle of manufacture (e.g., one or more computer program products)having, for instance, computer usable media. The media has therein, forinstance, computer readable program code means or logic (e.g.,instructions, code, commands, etc.) to provide and facilitate thecapabilities of the present invention. The article of manufacture can beincluded as a part of a computer system or sold separately.

Additionally, at least one program storage device readable by a machineembodying at least one program of instructions executable by the machineto perform the capabilities of the present invention can be provided.

The flow diagrams depicted herein are just examples. There may be manyvariations to these diagrams or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order, or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions and the like can bemade without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention as definedin the following claims.

1. A protection circuit for a parallel power system comprising aplurality of multi-phase voltage regulator modules (VRMs), eachmulti-phase voltage regulator module comprising a plurality of voltageregulators, wherein the plurality of multi-phase voltage regulatormodules are parallel coupled, the protection circuit comprising: atleast two separate isolation control circuits, each separate isolationcontrol circuit being coupled to a different multi-phase voltageregulator module of the plurality of multi-phase voltage regulatormodules of the parallel power system, and each separate isolationcontrol circuit comprising: a current sense circuit for sensing currentpolarity at an output of the respective multi-phase voltage regulatormodule; and a controller coupled to the current sense circuit forautomatically isolating the respective multi-phase voltage regulatormodule when an over-voltage condition exists at an output of theparallel power system and a positive current polarity is sensed at theoutput of the respective multi-phase voltage regulator module, whereinthe at least two isolation control circuits of the protection circuitisolate only a multi-phase voltage regulator module having positivecurrent outflow during the over-voltage condition, and anothermulti-phase voltage regulator module of the plurality of multi-phasevoltage regulator modules having negative current outflow during theover-voltage condition remains operational.
 2. The protection circuit ofclaim 1, wherein each separate isolation control circuit furthercomprises an isolation switch disposed at an input of the respectivemulti-phase voltage regulator module, wherein the controller is coupledto the isolation switch for automatically opening the switch to isolatethe respective multi-phase voltage regulator module when theover-voltage condition exists and positive current polarity is sensed atthe output of the respective multi-phase voltage regulator module. 3.The protection circuit of claim 2, wherein each isolation switchcomprises an isolation field effect transistor coupled between an inputpower line and the input to the respective multi-phase voltage regulatormodule, and each isolation field effect transistor is gated OFF by thecontroller when the over-voltage condition exists and the positivecurrent polarity is sensed at the output of the respective multi-phasevoltage regulator module.
 4. The protection circuit of claim 1, whereineach current sense circuit comprises a comparator having a first inputand a second input, the first input and the second input beingrespectively coupled to source and drain sides of an OR-ing field effecttransistor coupled to the output of the respective multi-phase voltageregulator module to sense current polarity through the OR-ing fieldeffect transistor.
 5. The protection circuit of claim 1, wherein eachseparate isolation control circuit further comprises an over-voltagedetection circuit for detecting when an over-voltage condition exists atthe output of the parallel power system, and wherein the controller iscoupled to the over-voltage detection circuit for receiving anover-voltage detection signal when the over-voltage condition exists atthe output of the parallel power system.
 6. The protection circuit ofclaim 5, wherein each over-voltage detection circuit comprises acomparator having a first input and a second input, the first inputbeing coupled to a reference voltage and the second input being coupledto the output of the parallel power system, wherein the over-voltagecondition exists when a voltage at the output of the parallel powersystem exceeds the reference voltage.
 7. A parallel power systemcomprising: a plurality of multi-phase voltage regulator modules (VRMs),each multi-phase voltage regulator module comprising a plurality ofvoltage regulators, wherein the plurality of multi-phase voltageregulator modules are coupled in parallel; and at least two separateisolation control circuits, each separate isolation control circuitbeing coupled to a different multi-phase voltage regulator module of theplurality of multi-phase voltage regulator modules of the parallel powersystem, and each separate isolation control circuit comprising: acurrent sense circuit for sensing current polarity at an output of therespective multi-phase voltage regulator module; and a controllercoupled to the current sense circuit for automatically isolating therespective multi-phase voltage regulator module when an over-voltagecondition exists at an output of the parallel power system and apositive current polarity is sensed at the output of the respectivemulti-phase voltage regulator module, wherein the at least two isolationcontrol circuits of the protection circuit isolate only a multi-phasevoltage regulator module having positive current outflow during theover-voltage condition, and another multi-phase voltage regulator moduleof the plurality of multi-phase voltage regulator modules havingnegative current outflow during the over-voltage condition remainsoperational.
 8. The parallel power system of claim 7, wherein eachseparate isolation control circuit further comprises an isolation switchdisposed at an input of the respective multi-phase voltage regulatormodule, wherein the controller is coupled to the isolation switch forautomatically opening the switch to isolate the respective multi-phasevoltage regulator module when the over-voltage condition exists andpositive current polarity is sensed at the output of the respectivemulti-phase voltage regulator module.
 9. The parallel power system ofclaim 8, wherein each isolation switch comprises an isolation fieldeffect transistor coupled between an input power line and the input tothe respective multi-phase voltage regulator module, and each isolationfield effect transistor is gated OFF by the controller when theover-voltage condition exists and the positive current polarity issensed at the output of the respective multi-phase voltage regulatormodule.
 10. The parallel power system of claim 7, wherein each currentsense circuit comprises a comparator having a first input and a secondinput, the first input and the second input being respectively coupledto source and drain sides of an OR-ing field effect transistor coupledto the output of the respective multi-phase voltage regulator module tosense current polarity through the OR-ing field effect transistor. 11.The parallel power system of claim 7, wherein each separate isolationcontrol circuit further comprises an over-voltage detection circuit fordetecting when an over-voltage condition exists at the output of theparallel power system, and wherein the controller is coupled to theover-voltage detection circuit for receiving an over-voltage detectionsignal when the over-voltage condition exists at the output of theparallel power system.
 12. The parallel power system of claim 11,wherein each over-voltage detection circuit comprises a comparatorhaving a first input and a second input, the first input being coupledto a reference voltage and the second input being coupled to the outputof the parallel power system, wherein the over-voltage condition existswhen a voltage at the output of the parallel power system exceeds thereference voltage.
 13. A method of protecting a parallel power supplycomprising a plurality of multi-phase voltage regulator modules (VRMs),each multi-phase voltage regulator module comprising a plurality ofvoltage regulators, wherein the plurality of multi-phase voltageregulator modules are coupled in parallel, the method comprising:providing a separate isolation control circuit for each respectivemulti-phase voltage regulator module of the at least two multi-phasevoltage regulator modules, each separate isolation control circuit:sensing current polarity at an output of the respective multi-phasevoltage regulator module; and automatically controlling isolation of therespective multi-phase voltage regulator module when an over-voltagecondition exists at an output of the parallel power system and apositive current polarity is sensed at the output of the respectivemulti-phase voltage regulator module, wherein only a voltage regulatorhaving positive current outflow during the over-voltage condition isisolated, and another multi-phase voltage regulator module of theplurality of multi-phase regulator modules having negative currentoutflow during the over-voltage condition remains operational.
 14. Themethod of claim 13, wherein the automatically controlling furthercomprises open circuiting an input of the respective multi-phase voltageregulator module when the respective multi-phase voltage regulatormodule has positive current outflow during the over-voltage condition.15. The method of claim 13, wherein the sensing comprises comparingsignals at source and drain sides of an OR-ing field effect transistorcoupled to the output of the respective multi-phase voltage regulatormodule to determine current polarity at the output.
 16. The method ofclaim 13, wherein each separate isolation control circuit furtherdetects when an over-voltage condition exists at the output of theparallel power system, said detecting comprising comparing a voltage atthe output of the parallel power system with a reference voltage, andwhen the voltage at the output of the parallel power system exceeds thereference voltage, signaling that an over-voltage condition exists. 17.The method of claim 13, wherein the providing comprises providing eachseparate isolation control circuit to be common to all phases of therespective, multi-phase voltage regulator module.